Extracted metallurgy generally involves the feeding of metal ore into a plasma heated stream of reducing gas. Generally, the feedstock comprises a mixture of metal oxide(s), hydrocarbonaceous material and flux. The metal oxide comprises the powdered ore to be treated, for example iron oxides such as taconite. When heated sufficiently, and provided in contact with a reductant, the material will reduce to the non-oxidized metal. Typically, the reduced metal material, in a molten state, drains to a bottom of the reactor, where it can be collected and drained.
The gas stream from the plasma torch comprises an ionized stream of reducing gas, typically carbon monoxide and hydrogen, at very high temperature, often 10,000.degree. F. or above. The metal oxides are fed into this stream, to be heated and reacted.
As previously indicated, for typical conventional operations the oxide is fed into the reactor in a feedstock stream, including hydrocarbonaceous material and flux. The hydrocarbonaceous material is typically a coal product. The hydrocarbonaceous material, in part, comprises the reductant which reacts with the heated oxides, to form carbon dioxide and water. Normal coal can be used for the carbonaceous material, however beneficiated coal is generally preferred. Beneficiated coal has a relatively high proportion of hydrogen to carbon content, while at the same time is low in moisture. The hydrocarbon or volatile fraction of beneficiated coal is high relative to other types of coal. For example, coal from the eastern part of the United States is generally low in volatiles, contains a relatively high percentage of aromatics, and is low in moisture content. Coal from the western part of the United States is generally high in volatiles, but also high in moisture. Beneficiated coal possesses the better, or more useful, characteristics of each.
Metal oxides include numerous silicates. The feedstock generally includes a flux therein, such as limestone, to reduce the melting temperature of the silicates, by forming calcium silicates. This facilitates the ore processing.
A plant for processing ore through utilization of a plasma torch generally comprises a reformer in communication with a reaction chamber or tower. The tower has a plasma torch mounted in an upper portion thereof, and a refractory lining. A feedstock comprising the metal oxides, carbonaceous material, and flux are generally fed, under gas pressure, into the plasma stream at or near the torch. The materials are heated substantially, and are blown outward from the torch area both downwardly and toward the refractory walls. Reducing gas in both the plasma torch and the gas used to propel the feedstock into the torch facilitates the reaction.
During the tower reaction, the metal oxides are reduced. The metal formed is typically hot enough to be molten and drips to the bottom of the tower into an awaiting crucible area from which it can be tapped. Slag material, such as silicates, may form on top of the pool of molten metal.
The gaseous products of the reaction generally comprise carbon dioxide and water. These gasses are directed through a reformer, packed with carbonaceous material. This process reduces the gasses, forming carbon monoxide and hydrogen. These gasses may then be collected and fed back into the plasma torch or the feedstock stream, as necessary.
Such conventional systems suffer from numerous problems. First, the refractory material lining the tower wall may be subject to considerable erosion or corrosion from hot feedstock material being thrown thereagainst, out of immediate proximity to the plasma torch. This results, in part, from the fact that the feedstock material is often fed directly into or near the hottest part of the torch area. Further, the metal oxides are only retained with the immediate proximity of the torch for a very brief period of time. Often this is so brief that the heated metal oxides cannot reach physical and chemical equilibria with the plasma gasses. That is, the oxides will not have been heated to as high a temperature as would be possible under a longer retention; and, further chemical reduction, which might have taken place in the plasma area had the retention time been longer, will have been inhibited.
Also, heating of the feedstock material in such systems is relatively energy inefficient, since the carbonaceous material and flux are also heated substantially by the plasma torch. That is, energy from the plasma torch is inefficiently used to heat the carbonaceous material and flux, when generally it is heating of the metal oxides that is most desired.
Further, as a result of dilution of the metal oxide with the flux and carbonaceous material, the zone immediately around the plasma torch is not as high in concentration of metal oxides as it might otherwise have been. Thus, only a relatively small amount of metal oxides can be passed through the torch zone at any given time.
Typical refractory materials comprise alumina or burnt chrome. The material is applied to the inside of a tower in a layer, in most instances about six inches to one foot thick. This is a relatively expensive liner, but one that has been necessary to withstand the extreme temperatures in the reaction tower. Often the expensive refractory material is backed by a lining of fire brick or the like, less efficient in retaining the heat but operable in most instances.
As previously suggested, when the heated metal oxides and other material are thrown against the refractory wall, erosion or corrosion occurs. This leads to damage of the refractory material, and a need for relatively frequent replacement. This is expensive not only in terms of material costs, but also in terms of plant down time, for servicing.
What has been needed has been a more efficient method of processing ore through the utilization of a plasma torch and reaction tower, and an apparatus for accomplishing such a method which is substantially less prone to the problems outlined.